The present invention relates to a gas laser with a closed gas channel wherein a gas flows at high velocity through a discharge chamber in which the gas discharge burns between at least two electrodes which extend transversely of the gas flow, and having for the maintenance of the gas flow a cross-current blower whose axis of rotation is parallel to the optical axis and whose buckets are disposed free-standing such that the gas stream flows twice through the bucket wheel. The delivery side of the blower is separated from its intake side on the inner wall of the gas channel by a baffle body extending in the same direction as the axis of the blower and reaching to the outer edges of the buckets, and such that the gas stream is fed from the delivery side through an approach channel to the discharge chamber.
A gas laser of this kind is disclosed both in GB-A 21 35 815 and in U.S. Pat. No. 4,686,680.
In transversely swept gas transport lasers, a cross-current blower is often used as the pump for circulating the laser medium, a type of blower which is well suited for this type of laser on account of its simple construction and its good volumetric output capacity. There is also the fact that the blower rotor extends parallel to the discharge over entire length of the latter, and due to the elimination of gas guiding means around axes perpendicular to the blower axis, a completely even sweeping of the entire laser cross section becomes possible. This leads to easily comprehensible bidimensional flow processes and to an uncomplicated scaling of the system in the direction of the optical axis without having to make basic changes in the flow system. With these cross-current blowers large-volume flows can be produced, but at relatively low pressure differences between the intake and discharge sides of the blower. Consequently the entire gas circuit of the laser must be so configured that the lowest possible pressure loss and the most uniform flow possible will be obtained with a low degree of turbulence so as not to provoke instability in the area of the electrical gas discharge.
Usually, blowers from the ventilation and air conditioning art are used, for example, but they are not designed either for the heavy throttling of the gas circuit that occurs in this case, nor for a low degree of turbulence. The main feature of these blowers is a high blowing efficiency, which, again, is of no interest in lasers operating in the lower-than-atmospheric pressure range. When severely throttled, the working points of these blowers are in the unstable part of their characteristic, which can signify especially great differences in the flow conditions over the length of the blower. It is typical of such cross-current blowers that, in the transition between the discharge and the intake side, which are separated from one another by baffles, an eddy forms which rotates in the same sense as the blower and passes partially through the buckets. If the throttling changes, the position of this eddy changes both against the direction of rotation of the blower and toward the interior of the blower. The blower characteristic, and hence the main characteristics of the blower, are determined by this eddy shift.
The gas laser described in GB-A 21 35 815 has a so-called cross-current blower in which the buckets are disposed substantially free-standing such that the gas stream passes twice through the bucket wheel. The gas channel on the delivery side of the blower is defined by a nose-shaped baffle body which partially surrounds the outer circumference of the buckets on the intake side of the blower. The gas channel carries the gas stream from the delivery side of the blower toward the discharge chamber, and this main channel tapers toward the discharge chamber.
In contrast to the laser of GB-A 21 35 815, in the laser of U.S. Pat. No. 4,686,680, instead of the nose-shaped baffle body on the delivery side of the laser, a thin sheet-metal baffle is used which separates the delivery side from the intake side of the blower. The free edge of this baffle reaches to the outer periphery of the buckets of the blower and is aligned with its tangents in the same direction as the axis of rotation of the blower.
As mentioned above, in such blowers turbulence is produced on the delivery side, which leads to irregularities in the flow. In particular, turbulence develops on the inner side of the channel in the area in which the wall defining the main channel reaches the buckets. Such turbulence continues under certain circumstances all the way to the discharge chamber.